The invention relates to a fuel injection pump for internal combustion engines, having a piston driven for simultaneous reciprocation and rotation and embodied both as a pump piston periodically pumping fuel and as a distributor piston rotatable in the guide bore; the piston has distributor openings discharging at its jacket face and communicating with various injection nozzles as a function of the rotational position of the distributor piston during the supply stroke of the pump piston.
German Patent 1 190 731 has disclosed a fuel injection pump operating on the distributor principle, which among other purposes can be used for direct injection of fuel into externally ignited internal combustion engines (Otto engines). The fuel furnished at pumping pressure by a work piston is distributed to the various injection valves by a distributor shaft that rotates at halt the rpm of the crankshaft. This known pump is arranged such that virtually simultaneously with the main injection that immediately precedes ignition, a pre-injection is performed into the working cylinder offset by 360.degree. of crankshaft rotation, or crankshaft angle. The amount of the pre-injection is less than that of the main injection.
One disadvantage of the known fuel injection pump is that neither the total amount of fuel injected nor the ratio of the amounts of the pre-injection and the main injection is variable. Nor can the supply onset or the end of supply be varied during operation, in the known apparatus. The known fuel injection pump is particularly unusable as a basis for modern fuel quantity control, because the pre-injection and the main injection have an effect on one another, resulting in insurmountable problems in fuel quantity distribution. Hydraulic pressure waves are a further factor making for imponderable metering.
In German patent application P 37 22 151.5, an object was to be able to perform the pre-injection and the main injection independently of one another, so that their influence on one another would not have to be a factor. To this end, the fuel injection pump was embodied as defined above, and the piston embodied as both a pump piston and a distributor piston acted via two separate work chambers, to enable separate regulation of the pre-injection and the main injection. The separate work chambers were defined by different faces of the piston and by the common guide bore, and the metering variously intended for the pre-injection and the main injection was enabled by separate magnetic valves. In this arrangement, the magnetic valves were switched in such a way that an opening of the valves terminated whichever injection event was taking place, i.e., either the main injection or the pre-injection.